Various tubular vessel structures within the human body, such as the biliary duct system, excretory system and vascular system, may deteriorate so that medical repair is necessary. For example, aortic aneurysms are abnormal ballooning out of the wall of the vessel, and put a person at risk of death from rupture of the aneurysm. These aneurysms most commonly involve the abdominal aorta just below the level of the arteries that supply the kidneys. The second most common location for such aneurysms is in the thoracic aorta, adjacent to the major branches which supply the head and arms.
Endovascular devices for repairing such aneurysms are known in the art. Several have been commercialized, including those made by Cook Vascular Incorporated of Vandergrift, Pa., W.L. Gore & Associates Inc. of Flagstaff, Ariz., Medtronic Inc. of Minneapolis, Minn. and Endologix, Inc. of Irvine, Calif. Such prior art devices are generally introduced through a vessel in the groin and tracked over a guidewire. The devices are typically introduced in a constrained condition, so as to allow access through the relatively smaller groin artery.
The prior art devices have significant similarities in terms of their overall structure. They are usually modular, in which a “main body” is introduced as one device, with a method of fixation and sealing incorporated into the proximate component, and an “ipsilateral limb”, which extends into the iliac artery. There is a “gate” as part of the main body, which is then cannulated from the contralateral groin so that a “contralateral limb”, a tubular stent-graft component, may be deployed to complete the two-piece endograft system.
In the thoracic aorta, the design is generally simpler, as the aorta does not branch over the course of the descending thoracic aorta. Hence there is only a single, tubular component to the endograft device.
In both the abdominal and thoracic aorta, the primary anatomic limitation to the success of aneurysm exclusion is the proximity of the major branch vessels to the aneurysm itself. The interval between the last major branch vessel and the aneurysm is referred to as the “neck.” Prior art devices generally specify in their Instructions For Use (IFU's) a minimum neck length for which each device is approved for use. Adequate neck length is critical for achieving a seal between the device and the normal aortic wall. If this length is too short, there may be insufficient wall contact to effectively exclude the aneurysm, leading to persistent flow in the aneurysm, or “endoleak”.
Unfortunately, the necks of both abdominal aortic aneurysms (AAA's) and thoracic aortic aneurysms (TAA's) are often too short for reliably successful endograft placement. In such cases, open surgical repair may be the only option. Many of the patients with AAA or TAA, however, have other conditions that make them very poor open surgical candidates, and hence no good option is available for their treatment.
In the past several years, many experimental techniques have been developed in an attempt to remedy this problem. These fall primarily into the categories of branched endografts and “fenestrated” endografts. Each involves a modified stent graft, with either holes created to align with the branch vessels (fenestrated), or pre-attached branch limbs which engage the branch vessels. In order to ensure proper alignment of these devices, extremely elaborate systems of guidewires are employed to pre-engage the branch vessels. This is a complex process which is beyond the skill set of many endovascular specialists, and makes such procedures difficulty to perform, lengthy, and more likely to produce complications.
In addition, all of the currently available endograft systems depend on a metallic endoskeleton for fixation, which is achieved through continuously outward frictional force generated by the spring-like metal. The metal, however, is relatively stiff, and hence does not conform well to the aorta when there is significant tortuosity of the vessel, or angulation of the vessel segments. Furthermore, the endografts fully supported by this metallic endoskeleton cannot be repositioned once deployed. Hence any malalignment of the endograft with side branches cannot be corrected, and this constitutes a potentially catastrophic limitation. For these reasons, adoption of fenestrated endografts has been extremely limited, and this has greatly limited the options available to a large subgroup of patients with life-threatening aneurysms.